1. Field of the Invention
The present invention relates to an electromagnetic pipe expanding inductor to be used for expanding a metallic pipe or the like which is an electric conductor by utilizing an electromagnetic force, as well as a method for manufacturing the same.
2. Description of the Related Art
According to the electromagnetic pipe expanding technique, an electric charge stored at a high voltage is discharged in an instant to an electromagnetic forming inductor to form a strong magnetic field around the inductor in an extremely short time and a workpiece is disposed within the strong magnetic field, thereby causing an electromagnetic reaction force to be created between the workpiece and a forming coil to expand the workpiece (Patent Literature 1).
The electromagnetic pipe expanding technique permits plastic working of electric conductors (e.g., Al, Cu, non-magnetic stainless steel, Ti) by utilizing an electromagnetic force and therefore can handle various shapes of workpieces, including pipe-like and plate-like workpieces. Accordingly, studies are being made about application of this technique to various fields.
As an electromagnetic pipe expanding inductor used in the electromagnetic pipe expanding technique there is known, for example, one disclosed in Patent Literature 2 or 3. FIG. 3 is a sectional view showing a conventional electromagnetic forming inductor disclosed in Patent Literatures 1 and 2. FIG. 3 illustrates a half portion from a central axis (a dot-dash line) of an electromagnetic pipe expanding coil to one peripheral surface.
As shown in FIG. 3, an electromagnetic pipe expanding inductor 101 has a bobbin 2 constituted like a shaft by insulating resin. A hollow conductor strand 4 of a rectangular section coated with a glass cloth tape 6 is wound spirally around the peripheral surface of the bobbin 2 as a center shaft to form a coil. A hollow portion 5 formed centrally of the conductor strand 4 functions as a refrigerant flowing path to cool the conductor strand 4. The conductor strand 4 is wound in such a manner that confronting surfaces of adjacent conductor strand 4 are parallel to each other. Further, glass cloth 7 is wound around the outside of the coil so as to have a predetermined thickness. Insulating resin 8 is impregnated into the glass cloth tape 6, glass cloth 7 and voids formed between constituents, thereby fixing the insulating layer and the conductor. The outer periphery of the glass cloth 7 is cut after the impregnation of the resin 8 so that the electromagnetic pipe expanding inductor 101 has a predetermined outside diameter.